A. Field of the Invention
The present invention relates generally to chemical analysis of aerosols, and, more particularly to a system and method for chemical analysis of individual particles in a high velocity gas flow using laser ablation ion mobility spectrometry.
B. Description of the Related Art
Time-of-flight mass spectrometry is a well-known technique for quickly and accurately providing ion mass information. Time-of-flight mass spectrometry systems accelerate ions, via an electric field, toward a field-free flight tube which terminates at an ion detector. In accordance with known time-of-flight mass spectrometry principles, ion flight time is a function of ion mass so that ions having less mass arrive at the detector more quickly than those having greater mass. Ion mass can thus be computed from ion flight time through the instrument.
Another known ion separation technique which may be used to separate the bulk of the ions in time is ion mobility spectrometry. Ion mobility spectrometry instruments typically include a pressurized static buffer gas contained in a drift tube which defines a constant electric field from one end of the tube to the other. Gaseous ions entering the constant electric field area are accelerated thereby and experience repeated collisions with the buffer gas molecules as they travel through the drift tube. As a result of the repeated accelerations and collisions, each of the gaseous ions achieves a constant velocity through the drift tube. The ratio of ion velocity to the magnitude of the electric field defines an ion""s mobility, wherein the mobility of any given ion through a high pressure buffer gas is a function of the collision cross-section of the ion with the buffer gas and the charge of the ion.
Time-of-flight mass spectrometry has the ability to simultaneously analyze all ions from each particle. This capability is also shared by other known mass spectrometry methods such as Fourier transform ion cyclotron resonance and quadruple ion trap. The disadvantages of these techniques is the need to operate under high vacuum conditions which adds complexity, size, and cost to the test instrument. Ion mobility spectrometry overcomes these limitations be permitting ion analysis to be performed at a pressure close to atmospheric pressure. Ion mobility spectrometry also retains the ability to simultaneously analyze all ions from each particle. However, there is a need in the art to analyze individual particles in a high velocity gas flow.
The present invention satisfies this need by providing a system and method for chemical analysis of individual particles in a high velocity gas flow. The present invention further provides an ion mobility spectrometry system and method that analyzes individual particles in a high velocity gas flow.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be learned from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the and combinations particularly pointed out in the appended claims.
To achieve the objects and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention comprises a system for chemical analysis of single particles in a high velocity gas flow, the system comprising: an ion source chamber; a laser for ablating the single particles in the high velocity gas flow entering the ion source chamber to produce positively- and negatively-charged ions from each single particle; means for extracting the positively-charged ions provided in the ion source chamber; means for extracting the negatively-charged ions provided in the ion source chamber; a first ion mobility spectrometer connected to the positively-charged ion extracting means and characterizing and detecting the positively-charged ions; and a second ion mobility spectrometer connected to the negatively-charged ion extracting means and characterizing and detecting the negatively-charged ions.
To further achieve the objects and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention comprises a method for chemical analysis of single particles in a high velocity gas flow, the method comprising the steps of: introducing the gas into an ion source chamber; ablating the single particles in the high velocity gas flow entering the ion source chamber with a laser to produce positively- and negatively-charged ions from each single particle; extracting the positively-charged ions from the ion source chamber; extracting the negatively-charged ions from the ion source chamber; characterizing and detecting the positively-charged ions with a first ion mobility spectrometer; and characterizing and detecting the negatively-charged ions with a second ion mobility spectrometer.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.